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Home / DTC / U0651 — Lost Communication With EGR Sensor A

U0651 — Lost Communication With EGR Sensor A

Detailed page for trouble code U0651.

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U0651

Generic U — Network/User

Lost Communication With EGR Sensor A

Brand: Generic
Type: U — Network/User
Views: UK: 13 EN: 25 RU: 20
AI status
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Page language: EN

Causes

  • Open, short, or intermittent wiring between EGR sensor A and its controller
  • Poor connector connection, corrosion, bent pins, or water intrusion at the sensor or harness connectors
  • Faulty EGR sensor/module or internal sensor electronics
  • Loss of reference power or ground to the sensor
  • CAN/LIN bus faults or other network communication errors
  • Failed or poorly programmed PCM/ECM or sensor module after replacement

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated (check engine light)
  • Reduced engine performance, hesitation, or rough idle if PCM enters limp mode
  • Reduced fuel economy or increased emissions
  • Possible lack of expected EGR operation (stiction or stuck valve) reported by other codes
  • Other modules reporting related U-codes or loss of multiple sensor data streams

What to check

  • Use an OBD-II scan tool to read U0651 and any additional stored codes and freeze frame data
  • Verify vehicle battery voltage and charging system are within specification
  • Check for other communication codes on the CAN/LIN bus (U0100, U0121, etc.)
  • Visually inspect the EGR sensor connector and harness for corrosion, damage, or loose pins
  • Wiggle the harness and connector while watching live data for intermittent changes
  • Confirm reference voltage and ground at the sensor connector with key on, engine off

Signal parameters

  • EGR sensor typically uses a 5 V reference and ground with a signal output proportional to valve position (typical signal ~0.5–4.5 V depending on position)
  • EGR temperature/pressure sensors (if used) will output a voltage or frequency corresponding to measured parameter
  • Network communication uses a two-wire differential bus (CAN) — normal resting voltages are near mid-supply (~2.5 V) on each CAN line; communication appears as differential signals on the bus
  • Expected: stable reference voltage, low-resistance ground, and a valid signal waveform when the EGR is actuated

Diagnostic algorithm

  1. Record all stored codes and freeze frame; note if U0651 is current or intermittent. Check for other network-related U-codes.
  2. Verify battery voltage (12.6 V+ at rest) and proper charging; low voltage can cause communication errors.
  3. Visually inspect sensor harness and connector for damage, corrosion, or water intrusion. Repair any obvious problems.
  4. With a good scan tool, attempt to view live data from the EGR sensor. If no data is present, verify power and ground at the sensor connector with key ON (reference ~5 V and chassis ground).
  5. Backprobe the sensor connector: confirm reference voltage, signal voltage, and ground. Wiggle harness and connectors while observing readings to find intermittent faults.
  6. If the sensor uses network communication (CAN/LIN), check bus integrity: measure CAN_H and CAN_L voltages at the connector (resting voltages near mid-supply) and verify termination resistance (~60 Ω across CAN_H and CAN_L). Use an oscilloscope if available to view messages.
  7. If power/ground and bus appear good but no valid signal, swap with a known-good EGR sensor (if applicable) or substitute a compatible sensor to verify behavior.
  8. If sensor replacement resolves communication failure, clear codes and test drive to confirm. If problem persists, investigate PCM/gateway for fault or perform software reflash/programming per manufacturer procedures.
  9. After repairs, clear codes and recheck to ensure U0651 does not return and related systems operate normally.

Likely causes

  • Corroded or loose connector at EGR sensor harness
  • Damaged wiring (chafing, pinched, rodent damage) on signal, power, or ground circuits
  • Failed EGR sensor or sensor module
  • Faulty CAN/LIN network termination or short between bus wires
  • PCM or gateway module fault or required software update/reflash

Fault status

⚠️ Status
U0651 — Lost Communication With EGR Sensor A. The control module is not receiving valid data from EGR Sensor A. May set MIL and affect emissions/EGR control. Investigate wiring, connectors, sensor, network, and module programming.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours
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